1. Field of the Invention
The present invention relates generally to a fluid-filled vibration damping device having a fluid chamber filled with a non-compressible fluid and constructed to provide a vibration damping effect based on flows of the fluid in the fluid chamber. More particularly, the present invention is concerned with such a fluid-filled vibration damping device which is novel in construction and suitably used in an engine mount, a body mount or other mounts for an automotive vehicle.
2. Description of the Related Art
As one type of a vibration damping device, such as a vibration damping coupling (bushing) or mount, which is interposed between two members of a vibration system for flexibly connecting these two members or mount one of these members on the other member in a vibration damping manner, there is know a fluid-filled vibration damping device which includes a first mounting member and a second mounting member which are spaced apart from each other and which are elastically connected to each other by an elastic body that partially defines a primary fluid chamber filled with a non-compressible fluid. The damping device further includes a partition structure supported by the second mounting member and flexible diaphragm which partially defines an auxiliary fluid chamber also filled with the non-compressible fluid, the volume of which is variable. The primary and auxiliary fluid chambers are located on the opposite sides ofthe partition structure, respectively, and communicated with each other through an orifice passage formed through the partition structure. Upon application of vibrational loads between the first and second mounting members, a pressure of the fluid in the primary fluid chamber changes due to elastic deformation of the elastic body, generating a pressure difference ofthe fluid between the primary and auxiliary fluid chambers. Based on this pressure difference of the fluid, the non-compressible fluid forcedly flows through the orifice passage between the primary and auxiliary fluid chambers, so that the vibration damping device exhibits an excellent vibration damping effect with ease, owing to resonance or flow of the fluid flowing through the orifice passage, which vibration damping effect is not attained by a non-fluid-filled type vibration damping device whose damping effect owing to only an elasticity of an elastic body thereof. In the light of this excellent vibration damping effect, the fluid-filled vibration damping device has been used as an engine mount for an automotive vehicle, for example.
Such a known fluid-filled vibration damping device as described above suffers from a problem of a significant increase of its dynamic spring constant upon application of vibrations having a frequency band higher than the frequency band to which the orifice passage is tuned, due to a significant increase of resistance to the fluid flow through the orifice passage. As a method to cope with this problem, it is proposed to constitute the partition structure by a combination of an annular orifice member which is fixedly supported by the second mounting member and which has an orifice passage extending in its circumferential direction along an inner circumferential surface of the second mounting member, and a flexible rubber plate which is supported at its peripheral portion by the inner peripheral portion of the annular orifice member such that the center opening of the orifice member is fluid tightly closed by the flexible rubber plate, for example. The thus constructed partition structure permits an effective formation of the orifice passage formed therein so as to extend its circumferential direction thereof, while allowing a substantive flow of the fluid between the primary and auxiliary fluid chambers, owing to the elastic deformation of the flexible rubber plate, upon application of a high frequency vibration. Therefore, the fluid-filled vibration damping device equipped with such a partition structure can exhibit its reduced dynamic spring constant, resulting in avoiding or reducing the undesirable significant increase of the dynamic spring constant of the device.
For fluid-tightly closing the center opening of the annular orifice member with the flexible rubber plate, JP-A-10-252813 disclosing a partition structure wherein the orifice member is constituted by a thick annular block member and the flexible rubber plate which is bonded at its peripheral portion to the inner circumferential surface of the orifice member. The orifice member in the form of the annular block has an inner circumferential surface whose area is enough large so that the flexible rubber plate is bonded to the inner circumferential surface of the orifice member with a sufficiently large bonding area. However, the orifice member needs to be formed of a metallic material by cutting or die-casting, resulting in low-efficiency and increased cost of manufacture of the orifice member.
Another partition structure of the fluid-filled vibration damping device is disclosed in JP-B-7-56314 wherein the partition structure is constituted by a combination of a plurality of metallic plates which are superposed on each other in the axial direction of the device in which the first and second mounting members are spaced apart from each other, and are fixedly secured together by press-fitting or welding. The metallic plates are partially bent so as to form the inner circumferential surface to which the outer periphery of the flexible rubber plate is bonded. This arrangement permits both of a sufficiently large bonding area of the flexible rubber plate and a efficient and economical manufacture of the orifice member by use of the metallic plates which are available at a relatively low cost and which permit excellent productivity. However, the partition structure consisting of the mutually press-fitted metallic plates may suffer from a problem of difficulty to assure with high stability a sufficient bonding strength at the interfaces of the metallic plates. On the other hand, the partition structure consisting of the mutually welded metallic plates may possibly suffer from a problem of deterioration or change of the property of the flexible rubber plates due to an adverse effect of heat upon welding the metallic plates to form the partition structure. Therefore, the conventional fluid-filled vibration damping device suffers from a problem of significant difficulty to assure a desired fixing strength of the orifice member and a desired elasticity of the flexible rubber plate, with high stability.
It is therefore an object of the invention to provide a fluid-filled vibration damping device having a partition structure which is novel in construction and easy and economical to manufacture, and which assures a sufficiently large bonding area of a flexible rubber plate with respect to an orifice member of the partition structure. The partition structure also permits a desired fixing strength of an orifice member, while exhibiting a desired elasticity of the flexible rubber plate with high stability.
The above object may be achieved according to the following modes of the invention each of which is numbered like the appended claims and depends from the other mode or modes, where appropriate, to indicate possible combinations of elements or technical features of the invention. However, it is to be understood that the present invention is not limited to those modes of the invention and combinations of the technical features, but may be otherwise recognized based on the thought of the present invention that disclosed in the whole specification and drawings or that may be recognized by those skilled in the art in the light of the disclosure in the whole specification and drawings.
(1) A fluid-filled vibration damping device comprising: a first mounting member and a second mounting member which are spaced-apart from each other, the second mounting member having a cylindrical portion open to the first mounting member; an elastic body elastically connecting the first and second mounting members and partially defining a primary fluid chamber filled with a non-compressible fluid; a partition structure which includes an annular orifice member having a central hole and being fixedly supported by the second mounting member, while defining an orifice passage extending along an inner circumferential surface of the cylindrical portion of the second mounting member in a circumferential direction thereof, and a flexible rubber plate fluid-tightly closing the central hole of the orifice member, the partition structure partially defines the primary fluid chamber on one of opposite sides thereof; and a flexible diaphragm partially defining an auxiliary fluid chamber which is filled with the non-compressible fluid, held in fluid communication with the primary fluid chamber through the orifice passage, and located on the other side of the partition structure which is remote from the primary fluid chamber, the orifice member including a first and a second annular components which are made of a metallic material by pressing and are superposed on each other in an axial direction thereof so as to define therebetween the orifice passage, the first and second annular components being fixed together such that an inner peripheral portion of the first annular component is bent to form a calking portion which is calked to an inner peripheral portion of the second annular member over a substantially entire inner circumference of the orifice member, the flexible rubber plate being bonded at an peripheral portion thereof to a surface of the calking portion in a process of vulcanization of a rubber material to form the flexible rubber plate.
In the fluid-filled vibration damping device according to the first mode (1) of this invention described above, the orifice member for defining the orifice passage for fluid communication between the primary and auxiliary fluid chambers, is constituted by first and second annular components which are fitted together by calking. This arrangement permits an improved efficiency and reduced cost of manufacture of the orifice member, in comparison with a conventional orifice member which is formed by cutting or die-casting. In addition, the present orifice member assures a sufficiently large strength thereof, in comparison with the conventional orifice member whose components are press-fitted to each other, while being free from a conventionally experienced problem such as a damage of the flexible rubber plate by heat undesirably applied to the flexible rubber plate upon welding the components of the orifice member. Moreover, the flexible rubber plate of the partition structure is bonded at its periphery to the surface of the calking portion of the orifice member which defines the inner circumferential portion of the orifice member, making it possible that the flexible rubber plate is bonded with an increased bonded area to the orifice member. It is noted that the orifice member may define partially the orifice passage, such that the first and second component cooperate to define a circumferential groove whose opening is closed by the second mounting member to define therebetween the orifice passage, for example. Alternatively, the orifice member may define completely the orifice passage, such that the first and second components cooperate to define therebetween the orifice passage.
While the peripheral portion of the flexible rubber plate is only required to be bonded to the surface of the calking portion of the one of the pair of annular components in the process of vulcanization of the rubber material to form the flexible rubber plate, it may be possible that the peripheral portion of the flexible rubber plate is bonded to the other part of the one and/or the other annular component, as well as the surface of the calking portion. It is noted that a specific length and a specific cross sectional area of the orifice passage defined by the orifice member are not particularly limited, but may be suitably dimensioned taken into account required vibration damping characteristic of vibration damping devices. For instance, the orifice passage may be formed so as to extend in the circumferential direction of the orifice member with a circumferential length which is slightly smaller than a value corresponding to the entire circumference of the orifice member, or alternatively be formed so as to extend spirally with a length which is longer than a value corresponding to the entire circumference of the orifice member.
(2) A fluid-filled vibration damping device according to the above mode (1), wherein radially outer portions of the first and second annular components extend radially outwardly, while being spaced-apart form each other in the axial direction thereof, so as to define therebetween an annular groove open in an outer circumferential surface of the orifice member, an opening of the annular groove being fluid-tightly closed by the cylindrical portion of the second mounting member to define therebetween the orifice passage.
In the above mode (2), each of the first and second annular components can be clamped at its outer peripheral portion, when the inner peripheral portion of these annular components are subjected to the calking operation. This arrangement facilitates handling and positioning of these components during the calking operation. It is preferably that the inner circumferential surface of the second mounting member is covered by a sealing rubber layer at a portion which is disposed radially outwardly on the opening of the annular groove, so that the opening of the annular groove is closed by the portion of the inner circumferential surface of the second mounting member with the sealing rubber layer sandwiched therebetween, thereby assuring an improved fluid-tight-sealing of the orifice passage.
(3) A fluid-filled vibration damping device according to the above mode (1) or (2), wherein the first annular components whose inner peripheral portion is bent to be calked to the inner peripheral portion of the second annular component has a wall thickness at least at the inner peripheral portion thereof which is made smaller than a wall thickness of the second annular component.
In the above mode (3), the inner peripheral portion of the first annular component can be easily bent owing to its reduced thickness, facilitating a bending operation with respect to the inner peripheral portion of the second annular component. This arrangement is effective to prevent occurrence of undesirable deformation of the second annular component due to an excess force acting thereon during the bending operation with respect to the first annular component, resulting in an improved efficiency of the bending operation and an improved strength of the orifice member resistive to load.
(4) A fluid-filled vibration damping device according to any one of the above modes (1)-(3), wherein the cylindrical portion of the second mounting member has an axially opposite open ends one of which is opposed to the first mounting member and is fluid-tightly closed by the elastic body, while the other open end of the cylindrical portion is fluid-tightly closed by the flexible diaphragm, such that the flexible diaphragm is bonded at its peripheral portion to a cylindrical fixing sleeve and is axially superposed at the cylindrical fixing sleeve on one of axially opposite surfaces of the orifice member of the partition structure, which is remote from the primary fluid chamber, and the cylindrical portion of the second mounting member being drawn onto and forcedly fitted onto outer circumferential surfaces of the orifice member of the partition structure and the cylindrical fixing sleeve.
In the above mode (4), the partition structure and the flexible diaphragm can be easily assembled with respect to the second mounting member by only inserting the partition structure and the flexible diaphragm the predetermined position of the second mounting member in this order from the other opening of the second mounting member. Further, the cylindrical fixing sleeve is forcedly fitted onto the inner circumferential surface of the second mounting member, thereby assuring an excellent fluid tight-sealing in the other open end of the second mounting member.
(5) A fluid-filled vibration damping device according to any one of the above modes (1)-(4), wherein the one of the first and second annular components has an engaging protrusion formed by pressing operation, while the other annular component has an engaging recess formed by pressing operation, the engaging protrusion and recess being engaged with each other so that the first and second annular components are positioned relative to each other in the circumferential direction thereof.
In the above mode (5), the provision of the engaging protrusion. and recess permits a stable positioning of the first and second annular components relative to each other, upon assembling the annular components together, even in the case where the pair of the annular components have specific positions for assembling thereof. These engaging protrusion and recess can be formed integrally with the respective annular components by pressing. That is, each of the annular components and the corresponding engaging protrusion or recess can be simultaneously formed by a single pressing operation.
(6) A fluid-filled vibration damping device according to any one of the above modes (1)-(5), wherein the first and second annular components are axially spaced-apart from each other at the radially outer portions thereof to define therebetween the orifice passage extending in the circumferential direction thereof, the first and second annular components being held in close contact with each other at respective circumferential positions in the radially outer portions thereof so as to form a blocking portion, in the radially outer portions thereof so as to form a blocking portion, so that the orifice passage is made discontinuous by the blocking portion in the circumferential direction thereof and extends in the circumferential direction with a circumferential length which is slightly smaller than a value corresponding to an entire circumference of the orifice member, the one of the first and second annular components further including a first communication hole formed therethrough, which is located on one of circumferential opposite sides of the blocking portion for fluid communication between one of opposite ends of the orifice passage and the primary fluid chamber, while the other annular component further includes a second communication hole formed therethrough, which is located on the other sides of the blocking position for fluid communication between the other end of the orifice passage and the auxiliary fluid chamber, the engaging protrusion being formed at the circumferential position of one of the first and second annular components, while the engaging recess being formed at the circumferential position of the other annular component. being axially spaced-apart from each other at the radially outer portions thereof to define therebetween the orifice passage extending in the circumferential direction thereof, the first and second annular components being held in close contact with each other at respective circumferential positions in the radially outer portions thereof so as to form a blocking portion, in the radially outer portions thereof so as to form a blocking portion, so that the orifice passage is made discontinuous by the blocking portion in the circumferential direction thereof and extends in the circumferential direction with a circumferential length which is slightly smaller than a value corresponding to an entire circumference of the orifice member, the one of the first and second annular components further including a first communication hole formed therethrough, which is located on one of circumferential opposite sides of the blocking portion for fluid communication between one of opposite ends of the orifice passage and the primary fluid chamber, while the other annular component further includes a second communication hole formed therethrough, which is located on the other sides of the blocking position for fluid communication between the other end of the orifice passage and the auxiliary fluid chamber, the engaging protrusion being formed at the circumferential position of one of the first and second annular components, while the engaging recess being formed at the circumferential position of the other annular component.
In the above mode (6), the pair of components cooperate to each other to define the orifice passage therebetween which extends in the circumferential direction with the circumferential length which is slightly smaller than the value corresponding to the entire of the circumference of the orifice member, without needing other members. In particular, the first and second components are desirably positioned relative to each other by means of the engaging protrusion and recess. Accordingly, the first and second communication hole can be suitably located at predetermined positions, respectively, resulting in a stable formation of the desired orifice passage.